Components having surfaces subject to wear during operation may need to be monitored during operation to ensure that an amount of wear does not exceed a threshold amount of permitted wear. Various arrangements and methods have been implemented to permit visual inspection of the wear. For example, markers have been embedded in the component material below the surface subject to wear. These markers may initially be visible, or they may be covered by the component material. As the component material wears the surface of the component moves until it reaches the marker. In some arrangements the marker may be characterized by a parameter that is different from the component material so that it is readily distinguishable from the component material. For example, the marker may exhibit a different color, making it readily identifiable. The marker may exhibit a different shape, or wear resistance. Upon further wear of the component material the surface and the marker typically wear together, and the different parameter may become more pronounced. For example, markers may exhibit more color, or different colors with increased wear.
Similarly, a marker's shape or its effect may become more pronounced with further wear. U.S. Pat. No. 7,278,519 to Iwai et al. discloses a brake having a first, softer material, and a second, harder material. The second material is a marker material that generates noise, indicating a certain level of wear. Further wear exposes more of the second, harder material, and hence generates more noise.
In a variation of the common arrangements, U.S. Pat. No. 6,932,891 to Wigg et al. discloses a marker becomes exposed upon loss of anode material, but is not lost as the anode material is lost.
However, due to the wide range of applicable uses and changing technologies, there remains room in the art to improve marker functionality.